1. Field of the Invention
The present invention relates to a piezoelectric electroacoustic transducer such as a piezoelectric sounder, piezoelectric speaker, piezoelectric receiver, or other such apparatus.
2. Description of the Related Art
Recently, in electronic equipment, home appliances, portable telephones, and other such apparatuses, a piezoelectric sounder, and piezoelectric speaker generating an alarm and operational cue signal have been widely used. In such piezoelectric electroacoustic transducers, a unimorph-type piezoelectric sounding body, in which a piezoelectric body made of a piezoelectric ceramic having electrodes disposed on the top and bottom surfaces is attached to one surface of a metal plate, is generally used. Furthermore, a piezoelectric electroacoustic transducer, in which a bimorph-type piezoelectric sounding body made of a piezoelectric ceramic of a laminated construction is used, has been proposed (see Japanese Unexamined Patent Application Publication No. 2001-95094).
FIG. 8 shows one example of a related piezoelectric electroacoustic transducer. The piezoelectric electroacoustic transducer includes a case 40, a cover 41, a piezoelectric sounding body 42, and terminals 43 and 44 which are insert-molded in the case 40. One end portion of the terminals 43 and 44 supporting both ends of the piezoelectric sounding body 42 is horizontally exposed at both ends of the inside of the case 40. The electrodes of the piezoelectric sounding body 42 are electrically connected to the terminals 43 and 44 by using a conductive adhesive 46, and the periphery portion of the piezoelectric sounding body 42 is fixed to the case 40 such that an elastic adhesive 47 of silicone rubber, etc., is coated over the electrodes. However, in this way, when the piezoelectric sounding body 42 is directly connected to the terminals 43 and 44 by using a conductive adhesive 46, both ends of the piezoelectric sounding body 42 are excessively restrained. As a result, the amount of displacement of the piezoelectric sounding body 42 is reduced which lowers the sound pressure.
Next, the applicant of the present invention has proposed a construction in which, as shown in FIG. 9, supporting portions 45 are provided at the inner portions of the case 40 inside the inserted terminals 43 and 44, the piezoelectric sounding body 42 is supported by the supporting portions 45, and the end surface of the piezoelectric sounding body 42 is covered by an elastic insulating material 48, and then a conductive adhesive is coated over the insulating material 48 between the piezoelectric sounding body 42 and the terminals 43 and 44. This device is disclosed in Japanese Patent Application No. 2001-193305 which was not published at the time of filing of this application. Moreover, after the conductive adhesive 46 has been coated, the periphery portion of the piezoelectric sounding body 42 is fixed to the case 40 by elastic adhesive (not illustrated). In this case, since both ends of the piezoelectric sounding body 42 are not excessively restrained by the case 40, the amount of displacement of the piezoelectric sounding body 42 increases and accordingly the sound pressure is increased.
A fixed length of the terminals 43 and 44 is required to be exposed inside the case 40 in order to ensure the conductivity to the conductive adhesive 46. However, when the supporting portions 45 for supporting the piezoelectric sounding body 42 are provided inside the terminals 43 and 44, the dimension S of the piezoelectric sounding body 42 is required to be reduced so as to be smaller by the exposed length of the terminals 43 and 44 than the dimension L of the case 40. In recent years, in keeping up with the demand for downsizing of electronic equipment, the miniaturization of piezoelectric electroacoustic transducers has also been required. Reducing the size of the case 40 means that the piezoelectric sounding body 42 is further reduced. When the dimension S of the piezoelectric sounding body 42 becomes smaller, the resonance frequency increases and the sound pressure is unfavorably reduced. Therefore, it is important that the dimensional difference between the dimension L of the case 40 and the dimension S of the piezoelectric sounding body 42 is kept as small as possible.